When you click the Reply button, there is an Attachments and other options link, this expands the options to attach a file, that can be an image file or a text file (.log or .txt), see image below (click to expand).
- When you click the Reply button, there is an Additional Options link, this expands the options to attach a file, that can be an image file (.gif, .jpg or .png) or a text file (.log or .txt).